Hey guys, I'm planning on purchasing some R-1 Racing guages to keep me informed of every aspect of my engine but I don't know what the hell some of them are for.. all I really understand is the boost one.. I need to know what purpose do the following gauges serve..

-water temp.
-exhaust temp.
-oil pressure
-air/fuel ratio
-temp.
-amp meter
-volt meter

If possible, can someone please tell me why I need to know the following things and how they will help my engine/performance.. Also, besides boost, which ones are the most important.. thanks a lot guys..